Recently, vigorous attempts to develop an active matrix-type liquid crystal display (LCD) device in which thin film transistors are incorporated as switching elements for driving the liquid crystal have been conducted.
One example of such LCD device is illustrated by a schematic plan view of FIG. 6. On a substrate 31 made of glass or quartz, a gate driver 32, a source driver 33, and a TFT (thin film transistor) array section 34 are installed. The gate driver 32 is composed of a shift register 32a and a buffer 32b. The source driver 33 is composed of a shift register 33a, a buffer 33b, and analog switches 39 for sampling video lines 38. In the TFT array section 34, there are provided a plurality of gate bus-lines 116 which originate from the gate driver 32 and are parallel to each other. A plurality of source bus-lines 120 originate from the source driver 33, and extend so as to orthogonaly cross the gate bus-lines 116. Besides, additional capacity common lines 114 are provided parallel to the gate bus lines 116.
In each rectangular region surrounded by two gate bus-lines 116, two source bus-lines 120, and two additional capacity common lines 114, there are provided a TFT 35, a pixel 36, and an additional capacity 37. A gate electrode of the TFT 35 is connected with one of the gate bus-lines 116, while a source electrode thereof is connected with one of the source bus-lines 120. Liquid crystal is sealed into between a pixel electrode connected with a drain electrode of the TFT 35 and a counter electrode on a counter substrate, thereby constituting the pixel 36. The additional capacity common line 114 is connected to an electrode having the same potential as that of the counter electrode.
Usually, on an inner surface of the counter substrate, there are provided a black matrix to prevent light from leaking from gaps between the pixel electrodes, as well as color filters of red color (color R), color filters of green color (color G), and color filters of blue color (color B) which correspond to pixel electrodes, respectively. On top of the black matrix and the color filters, the counter electrode is provided, which is composed of a transparent conductive film. Thus, in the case where the black matrix and the color filters are provided on the counter substrate, it is necessary to form the black matrix larger than a desired size, since an assembling error tends to occur when the TFT substrate and the counter substrate are combined. As a result, an aperture ratio decreases. In the case where the color filters are formed on the counter substrate, it is necessary to form color filters to a required shape and size accurately. Therefore, a photo-lithography process is required, thereby raising a manufacturing cost.
To solve this problem, providing the color filters on the TFT substrate has been proposed, as is in the Japanese Publication for Laid-Open Patent Application No.5-5874/1993 (Tokukaihei No.5-5874). This is a method for forming filters of the colors R, G, and B on the pixel electrodes not by the photo-lithography process but by the electro-deposition process. In this conventional case, scanning voltages are sequentially applied to the gate bus-lines so that the pixel electrodes are subjected to application of voltages, while in synchronization with this, voltages for forming electro-deposited color filters on the correspondent pixel electrodes are applied to the source bus-lines. Thus, at each step of the sequential selection of the gate bus-electrode, one gate bus-line is selected and a voltage is applied from the source bus-lines to certain pixel electrodes among the pixel electrodes connected to the selected gate bus-line. As a result, electro-deposited color filters are formed on the pixel electrodes to which the voltage has been applied.
However, in the aforementioned conventional case, it is required to apply signals sequentially to the gate bus-lines and the source bus-lines, and for this purpose, it is necessary to make the gate driver and the source driver operate. Therefore, many signals have to be supplied to the drivers, thereby making the color filter formation process complicated.
Specifically, regarding a driver-incorporated LCD device in which the drivers and the TFT array are provided on the same substrate, since the drivers are made of polycrystalline silicon which has less mobility as compared with monocrystal, a plurality series of shift registers are provided so that the shift registers may respectively have lower operational frequencies. By doing so, the LCD device in which drivers made of polycrystalline silicon are integrated is realized, as disclosed in the Japanese Examined Patent Publication No.5-22917/1993 (Tokukohei No.5-22917). For example, in order to drive an LCD device with not less than 800 signal lines by the use of an element made of polycrystalline silicon with a mobility of about 100 to 150 (cm.sup.2 /v.multidot.sec), the element should be equipped with at least four series of shift registers, or preferably, eight series of shift registers.
FIG. 7 illustrates an arrangement example wherein four series of shift registers 331 through 334 are provided in the source driver 33 so that each operational frequency of the shift registers is lowered. In FIG. 7, the gate driver 32 and the source driver 33 are connected with the TFT array section 34. The shift registers 331 through 334 provided in the source driver 33 are connected with every four source bus-lines, respectively, through analog switches 39. Besides, three video lines 38, for example, are connected with each analog switch 39.
As to the shift registers 331 through 334, it is necessary to supply, for example, the shift register 331 with at least a start pulse SP, a clock signal CK1, and an signal /CK1 which is an inverted signal of the signal CK1, and to supply the shift register 332 with at least a start pulse SP, a clock signal CK2, and a signal /CK2 which is an inverted signal of the signal CK2. The other shift registers should be similarly arranged.
Therefore, in the case where there are provided eight series of shift registers, 2.times.8=16 clock signals should be supplied solely to the shift register series, thereby making a device for supplying the signals complicated. Moreover, similarly, start pulses SPG, clock signals GCK, and signals /GCK which are inverted signals of the clock signals GCK are supplied to the gate driver 32.
Furthermore, in the case where color filters are formed by the use of the drivers for driving the LCD device, the following occur: after such costly drivers are connected with a substrate, the drivers are damaged by static electricity through a later process, for example, through a rubbing process, and hence the drivers have to be removed. Thus, this method has a drawback in that the same drivers are not used in the LCD device.
Another method for forming the color filters is disclosed by the Japanese Publication for Laid-Open Patent Application No.3-87702/1991 (Tokukaihei No.3-87702). This is a method whereby a voltage is simultaneously applied to a group of pixels on which color filters of one same color are provided, so that the color filters of the same color are formed in a single step.
However, in the conventional case, the gate bus-lines, source bus-lines corresponding to pixels of the color R, source bus-lines corresponding to pixels of the color G, and source bus-lines corresponding to pixels of the color B are at least separately provided when the electro-deposited color filters are formed, and three signal input terminals are needed for supplying signals for color filter formation. Therefore, in respective color filter formation processes for the colors R, G, and B, it is required to supply signals to different signal input terminals, and hence it is required to switch the input terminals before the second color filter formation process and before the third color filter formation process, respectively.
Furthermore, in none of the conventional cases, consideration is taken regarding a method for forming light shielding films on the TFTs.
In the aforementioned conventional case, in order to form a plurality of TFT substrates out of one substrate, it is required to repeat the color filter formation process three times respectively for the colors R, G, and B with respect to every TFT substrate. Therefore, in the case where, for example, three TFT substrates are formed out of one substrate, the color filter formation process has to be repeated 9 times (=3 (colors R, G, and B).times.3 (substrates)).
As mentioned before, in the aforementioned conventional case, it is required that the gate bus-lines, source bus-lines corresponding to pixels of the color R, source bus-lines corresponding to pixels of the color G, and source bus-lines corresponding to pixels of the color B are at least separately provided when the electro-deposited color filters are formed. However, in the case where the bus-lines are separately provided in a previous process or a subsequent process, the TFTs are damaged, for example, by static electricity, and such breakdown of the TFTs leads to dot-like display defects in a display section of the LCD device.